Intra-aortic balloon catheter having a dual sensor pressure sensing system

ABSTRACT

A balloon catheter having a micromanometer connected to the catheter and also a fluid-filled transducer system for adjusting micromanometer pressure measurements.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a catheter having enhanced pressuresensing capabilities. More particularly, the invention relates to aballoon catheter having a micromanometer connected to the catheter andalso a fluid-filled transducer system for adjusting micromanometerpressure measurements.

[0003] 2. Description of the Prior Art

[0004] A key function of many catheters is that of continuouslymonitoring blood pressure. In many cases, this monitoring must beperformed with accurate measurement of high frequency components. Forexample, reliable detection of the dicrotic notch of the aortic bloodpressure waveform typically requires a pressure signal having abandwidth of 15 Hz or better. Detection of the dicrotic notch isgenerally used for the inflation/deflation timing of an intra-aorticballoon (“IAB”) catheter.

[0005] Conventional invasive pressure monitoring is performed withlow-cost fluid-filled transducers. A typical disposable monitoring kit,inclusive of all tubing, a continuous flush device, and a pre-calibratedtransducer is very affordable. Unfortunately, these systems have severaldrawbacks. One major drawback is that bubbles or clots in the monitoringlines can reduce the frequency response of the system to a level below15 Hz, creating an “overdamped” condition. In other cases, thecharacteristics of the catheter and tubing can result in “ringing”,which is associated with an underdamped condition. Furthermore,fluid-filled catheters can suffer from “catheter whip” (motionartifact), which is manifested as one or more high frequency deflectionsin the pressure signal. These problems can degrade the usefulness of thesignal in applications such as intra-aortic balloon pumping (IABP). Inparticular, it is difficult, if not impossible, to automatically provideoptimal timing of IABP using a pressure signal with a frequency responsebelow 15 Hz, or using signals with ringing or whip artifacts that mimicthe physiologic dicrotic notch.

[0006] Another means for monitoring blood pressure is to use amicromanometer, such as marketed by companies such as Millar,Endosonics, and Radi. See U.S. Pat. Nos. 5,431,628 and 5,902,248, hereinincorporated by reference. These devices can have excellent frequencyresponses, with system bandwidths greater that 200 Hz. They are notsubject to the negative effects of bubbles and catheter whip, and retaingood performance even in the presence of small blood clots.Unfortunately, they are very expensive, prone to signal drift, and cansuffer from electrical interference. A common source of electricalinterference in the setting of IABP therapy is the use ofelectrosurgery. In this situation, it is desirable to maintain areliable pressure signal with which to trigger the balloon, as the ECGsignal which normally triggers IABP operation becomes completelyunreliable. Conventional fluid-filled transducer systems are relativelyimmune from this type of interference.

[0007] If the above problems were solved, micromanometers couldpotentially be used in conjunction with IABP systems and other cathetersto measure blood pressure. Attempts have been made to usemicromanometers for IABP timing, see U.S. Pat. Nos. 3,585,983 and4,733,652, herein incorporated by reference. These attempts proved to beunreliable, as the device may be damaged during insertion and is alsoprone to signal drift. To address the drift issue, U.S. Pat. No.5,158,529, herein incorporated by reference, discloses a method forrezeroing the micromanometer by using the pressure from a partiallyfilled balloon as it rests in the aorta. However, this method requiresmomentary interruption of IABP, which may be harmful to the criticallyill patient.

[0008] While standard IAB catheters incorporating a fluid-filledtransducer pressure measurement system or IAB catheters incorporatingmicromanometers may be suitable for the particular purpose employed, orfor general use, they would not be as suitable for the purposes of thepresent invention as disclosed hereafter.

SUMMARY OF THE INVENTION

[0009] Accordingly, there is a need for a reliable and affordablepressure monitoring approach that has high bandwidth pressure sensing,low signal drift, and freedom from electrosurgical interference. Thereis also a need to incorporate this technology into intra-aortic ballooncatheters having small cross sectional profiles.

[0010] The invention is an IAB catheter system having enhanced bloodpressure sensing capability. The IAB catheter has a micromanometer, orany high fidelity sensor, built into the tip of the IAB or connected toanother part of the catheter, and a fluid-filled transducer kitconnected to the y-fitting of the IAB. The IABP console, including aprocessor, continuously monitors and compares signals from both themicromanometer and the fluid-filled transducer. The signal from themicromanometer may be continuously displayed, and either continuously orintermittently adjusted for baseline drift by comparing it to that ofthe fluid-filled transducer. The adjustment is preferably made bycomparing mean blood pressures as indicated by the two sources.

[0011] The IABP console could also monitor the micromanometer's signalfor the presence of electrosurgical interference, mechanical damage, orany other possible causes of signal error. If significant errors aredetected, the system automatically reverts to the use of the signal fromthe fluid-filled transducer system. The system also allows the user tomanually select the use of the fluid-filled transducer, in the eventthat electrosurgical interference was anticipated.

[0012] To the accomplishment of the above and related objects theinvention may be embodied in the form illustrated in the accompanyingdrawings. Attention is called to the fact, however, that the drawingsare illustrative only. Variations are contemplated as being part of theinvention, limited only by the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the drawings, like elements are depicted by like referencenumerals. The drawings are briefly described as follows.

[0014]FIG. 1 is a perspective view of the system of the presentinvention.

[0015]FIG. 2 is a detailed longitudinal cross sectional view of flushdevice 34 in FIG. 1.

[0016]FIG. 3 is longitudinal cross sectional view of a distal portion ofIAB catheter 10 in FIG. 1.

[0017]FIG. 3A is a perspective view of distal end of inner tube 58,shown independent of catheter 10, with pressure sensing line 24connected to an outer surface of inner tube 58.

[0018]FIG. 3B is a perspective view of a distal end of inner tube 58,shown independent of catheter 10, with pressure sensing line sandwichedbetween an outer surface of inner tube 58 and an outer layer.

[0019]FIG. 3C is a perspective view of a distal end of inner tube 58,shown independent of catheter 10, with pressure sensing line 24 embeddedin the wall of inner tube 58.

[0020]FIG. 4 is a longitudinal cross sectional view of a distal portionof a co-lumen IAB catheter having a pressure sensor embedded in the tip.

[0021]FIG. 4A is a transverse cross section of the co-lumen IAB, takenalong lines 4A-4A in FIG. 4.

[0022]FIG. 5A is a perspective view of a distal end of the inner tube 58and the catheter pressure sensor 22, illustrating a first connectionscheme.

[0023]FIG. 5B is a perspective view of a distal end of the inner tube 58and the catheter pressure sensor 22, illustrating a second connectionscheme.

[0024]FIG. 5C is a perspective view of a distal end of the inner tube 58and the catheter pressure sensor 22, illustrating a third connectionscheme.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025]FIG. 1 illustrates the system of the present invention comprisingan intra-aortic balloon (“IAB”) catheter 10, an intraaortic balloon pump(“IABP”) 12, a monitor 14, a drip bag 16, and a drip bag holder 18. FIG.1 is a perspective view of the system with the IAB catheter 10 in theforeground and the IABP 12 is the background for clarity. The IABcatheter 10 contains a catheter pressure sensor 22 connected to its tip20 and a Y-fitting 36 on its proximal end. The catheter pressure sensor22 is connected to the IAB pump 12 via pressure sensing line 24, shownas ghost lines in the IAB catheter 10. Inflate/deflate tube 26,connecting an outer lumen of the IAB catheter 28 (see FIGS. 3-4) and theIABP 12, is used for inflation and deflation of a balloon membrane 30connected between the tip 20 and a distal end of the IAB catheter 10.Drip tube 32 connects the pressurized drip bag 16 to a flush device 34.Saline tube 38 connects the flush device 34 with an inner lumen 60 ofthe IAB catheter (see FIGS. 3-4). Clamp 40 connects the flush device 34to the drip bag holder 18.

[0026] The details of flush device 34 can be seen in FIG. 2. The flushdevice 34 comprises a flush device wall 52, a microbore passage 42, afast flush seal 44 having a handle 46, flush device lumen 48, and a fastflush variable lumen 50. Pressure sensor 40 is located in flush device34 and communicates with IABP 12 via an independent line (not shown),which may exit through a hole (not shown) in flush device wall 52, or inany other means known in the art for electrical devices to communicate.Saline, or another appropriate working fluid or gas, flows through theflush device lumen 48 through the microbore passage 42 at a very slowrate, approximately 3 cc/hour. The pressure on the side of the flushdevice 34 connected to drip bag 16 equals the pressure in the drip bag16, generally 300 mmHg. The pressure on the opposite side of the flushdevice 34 adjacent the pressure sensor 40 equals the blood pressure ofthe patient being treated with the IAB catheter 10. The fast flush seal44 is shown in an open state, however, during therapy fast flush seal 44is forced against seat 54 by the flush device wall 52, and therefore,does not allow saline through fast flush variable lumen 50. In order tofast flush saline tube 38 and bypass microbore passage 42, handle 46 canbe pulled away from the flush device 34 such that fast flush seal 44 islifted off seat 54. During normal operation, however, saline drip isforced through microbore passage 42. Note that the flush device 34 maybe replaced with any other known flush device in the art having similarfunction.

[0027] The IABP 12 has incorporated therein a processor which controlsthe inflation/deflation timing of the balloon membrane 30.Alternatively, the IABP 12 can be connected to a computer or any othertype of control mechanism known in the art. The IAB catheter 10 istypically inserted into the femoral artery and moved up the descendingthoracic aorta until the distal tip 20 is positioned just below ordistal to the left subclavian artery. The proximal end of the catheterremains outside of the patient's body. The patient's central aorticpressure is used to time the inflation and deflation of balloon membrane30 and the patient's ECG may be used to trigger balloon membrane 30inflation in synchronous counterpulsation to the patient's heartbeat.

[0028] In the preferred embodiment, IABP 12 continuously monitors andcompares signals from both saline pressure sensor 40 and catheterpressure sensor 22. The signal derived from catheter pressure sensor 22may be continuously displayed on monitor 14 and either continuously orintermittently adjusted for baseline drift or other errors by comparingit to that of saline pressure sensor 40. The adjusted signal isdisplayed on monitor 14 and is used to time the inflation and deflationof the balloon membrane. The balloon membrane is inflated coincidentwith closure of the aortic valve and is contracted or deflated prior tocardiac ejection.

[0029] It is preferred that the adjustment be made by comparing meanblood pressures as indicated by the two sources. In operation pressurewould be measured over a predetermined period of time via both thecatheter pressure sensor 22 and the saline pressure sensor 40. Anindicated mean pressure, based on the catheter pressure sensor 22measurements, and a true mean pressure, based on the saline pressuresensor 40 measurements, are calculated. If the indicated mean pressurediffers from the true mean pressure by less than a predetermined amount,the catheter pressure sensor 22 measurements are displayed withoutcorrection; otherwise the catheter pressure sensor measurements arecorrected prior to display such that the indicated and true meanpressures are equal. Alternatively, the pressures can be compared on acontinuous point-by-point basis and an adjustment made if and when apredetermined pressure differential is reached.

[0030] IABP 12 may be programmed to provide options as to which sensoris relied on in any given situation and as how to compare the signalsfrom both sensors and use the information contained in these signals tomost accurately measure blood pressure. Note also, that in analternative embodiment of the invention, a pressure cuff or otherexternal or internal independent device known in the art may replace oract as a backup to the saline pressure sensor 40. The reading from theindependent external or internal blood pressure measurement device maybe used to correct the drift in the catheter pressure sensor 22 readingin the same manner as used with the saline pressure sensor 40 reading.Use of such an independent external or internal measurement device maybe necessary to adjust for drift in tip sensors in intraaortic catheterswithout an inner tube and associated saline pressure sensor.

[0031] The adjustment to the catheter pressure sensor 22 readings, asdescribed above, involves comparing mean blood pressures. Other methodsof adjustment may include comparisons of diastolic pressures, systolicpressures, pressures at the end of balloon inflation, andballoon-augmented pressures. The IABP 12 may also monitor the signalfrom catheter pressure sensor 22 for the presence of electrosurgicalinterference, mechanical damage, or any other possible cause of signalerror. If significant error is detected, the IABP 12 would automaticallyrevert to use of the signal from saline pressure sensor 40. Similarly,the IABP 12 may monitor the signal from the saline pressure sensor 40for errors and compensate for these errors by using the signal from thecatheter pressure sensor 22. The IABP 12 may optionally allow a user tomanually select the use of the saline pressure sensor 40 or the catheterpressure sensor 22. Use of the saline pressure sensor 40 may bedesirable in the event that electrosurgical interference wasanticipated.

[0032] In an alternate embodiment of the invention, rather thanadjusting the saline pressure sensor 40 signal for drift, the catheterpressure sensor 22 signal may be used solely for numerical displaypurposes and the catheter pressure sensor 22 signal used solely fortiming the inflation and deflation of balloon membrane 30.

[0033] Catheter pressure sensor 22 may include any type of sensorcapable of fitting on the catheter and of measuring blood pressure andproducing a signal with a frequency response above approximately 15 Hz.Such sensors include but are not limited to micromanometers such asthose produced by companies such as Millar, Endosonics, and Radi. Thesesensors typically include a small transducer exposed to arterialpressure on one side and often a reference pressure on the oppositeside. Blood pressure deforms the transducer resulting in a change inresistance which is translated into a pressure reading. Alternatively, afiber optic sensor may be used in which case pressure sensing line 24would comprise a fiber optic line. Co-pending application, entitledIntra-Aortic Balloon Catheter Having a Fiberoptic Sensor, filed on Dec.11, 2000, herein incorporated by reference in its entirety, disclosesspecific embodiments of an intra-aortic balloon catheter having anincorporated fiberoptic sensor.

[0034] The present invention, namely the dual use of both a fluid columnpressure sensor and a secondary sensor to measure arterial pressure, isnot limited for use with any specific type of catheter. Furthermore, useof different types of intra-aortic balloon catheters is anticipated.FIG. 3 illustrates a longitudinal cross section of a distal portion of atypical dual lumen intra-aortic balloon (“IAB”) catheter 10 comprisingan outer tube 56, an inner tube 58, a tip 20, and a balloon membrane 30connected on one end to the outer tube 56 and on the opposite end to thetip 20. Tip 20 defines a tip lumen 21. The inner tube 58 is disposedwithin the outer tube 56 and is connected to the tip 20 at its distalend. The inner tube 58 defines an inner lumen 60 and the outer tube 56defines an outer lumen 28. Inner lumen 60 communicates with saline tube38 and is filled with saline or another suitable fluid for pressuresensing (see FIG. 1). Outer lumen 28 is used for shuttling helium oranother appropriate working gas or fluid for inflation and deflation ofthe balloon membrane 30. The outer tube 56 may be coil or braidreinforced and made from polyurethane or polyimide. Inner tube 58 may bemade from polyimide or an alloy with shape memory and superelasticproperties commonly referred to as Ni—Ti, NITINOL™, and other industrynames. Inner tube 58 may be connected to an inner surface of the outertube 56 at one or more points or along the entire length of outer tube56 to enhance pushability, stability, pumping speed, and pressurefidelity. Catheter pressure sensor 22 is embedded in or attached to tip20.

[0035] Pressure sensing line 24 connects catheter pressure sensor 22 toIABP 12 and is sandwiched between the outer surface of inner tube 58 anda secondary layer 64. Alternatively, the pressure sensing line 24 isembedded in inner tube 58 or attached to the outer surface of inner tube58 or (see discussion of FIGS. 3A-3C below). Pressure sensing line 24will vary dependent on the type of sensor used. If an electricalmicromanometer of half-bridge design is used pressure sensing line 24may consist of three fine wires 62 (see FIGS. 3A-3C), each approximately0.001 inches in diameter. Note that the catheter pressure sensor 22 maybe positioned in alternate locations along IAB catheter 10 as well as ona distal tip of an independent catheter that can be disposed within theinner lumen 58. Dotted box, labeled A, designates another area where thecatheter pressure sensor 22 may be located. In this location catheterpressure sensor 22 is exposed to arterial pressure via tip lumen 21 andis less likely to be damaged upon insertion and placement of IABcatheter 10.

[0036] FIGS. 3A-3C illustrate transverse cross sections of inner tube 58with pressure sensing line 24 connected to inner tube 58 in variousconfigurations. In FIG. 3A, pressure sensing line 24, comprising threefine wires 62, is connected to an outer surface of inner tube 58. InFIG. 3B, pressure sensing line 24 is disposed between inner tube 58 anda thin walled tube 64, which preferably is heat shrinkable. In FIG. 3C,pressure sensing line 24 is embedded in the wall of inner tube 58. Notethat although pressure sensing line 24 is shown running along alongitudinal axis of inner tube 58 it may also be wound helically.

[0037]FIG. 4 illustrates a distal portion of another embodiment of theIAB catheter 10, comprising a balloon membrane 30, a tip 20, a co-lumentube 56, an inner lumen extension tube 66, and a catheter pressuresensor 22. Detailed structure of a co-lumen IAB is disclosed in U.S.Pat. No. 6,024,693 and U.S. patent application Ser. No. 09/412,718,filed on Oct. 5, 1999, both herein incorporated by reference. Tip 20 isconnected to a distal end of the balloon membrane 30 and to a distal endof the inner lumen extension tube 66. Tip 20 defines a tip lumen 21. Adistal end of the co-lumen tube 56 is connected to a proximal end of theballoon membrane 30 and to a proximal end of the inner lumen extensiontube 66. The co-lumen tube 56 may be coil or braid reinforced and madefrom polyurethane or polyimide. The preferred material for inner lumenextension tube 66 is an alloy with shape memory and superelasticproperties commonly referred to as Ni—Ti, NITINOL™, and other industrynames. Inner lumen extension tube 66 may also be made from polyimide.The catheter pressure sensor 22 is attached to tip 20 and pressuresensing line 24 which communicates signals generated by the catheterpressure sensor 22 to the IABP 12 (see FIG. 1).

[0038] Pressure sensing line 24, as illustrated in FIG. 4, is sandwichedbetween inner lumen extension tube 66 and thin walled tube 64; however,pressure sensing line 24 may be connected to the inner lumen extensiontube 66 in any of the ways illustrated in FIGS. 3A-3C. It is preferredthat pressure sensing line 24 float freely in outer lumen 28, asillustrated in FIG. 4, however, pressure sensing line 24 may beconnected to co-lumen tube 56 in any of the ways illustrated in FIGS.3A-3C. FIG. 4A illustrates a transverse cross section of outer tube 56,taken along line 4A-4A illustrated in FIG. 4, with pressure sensing line24 embedded in the wall. Note that pressure sensing line 24 may beembedded at a different location in co-lumen tube 56 or connected to asurface of co-lumen tube 56.

[0039] Co-lumen tube 56 defines two distinct lumens, inner lumen 60 andouter lumen 28. Inner lumen 60 communicates with saline tube 38 (seeFIG. 1). Outer lumen 28 communicates with inflate/deflate tube 26 and isused for shuttling helium or another appropriate fluid or gas forinflation and deflation of balloon membrane 30. Note that the catheterpressure sensor 22 may be positioned in alternate locations along IABcatheter 10 as well as on a distal tip of an independent catheter thatcan be disposed within the inner lumen 58. Dotted box, labeled A,designates another area where the catheter pressure sensor 22 may belocated. In this location catheter pressure sensor 22 is exposed toarterial pressure via tip lumen 21 and is less likely to be damaged uponinsertion and placement of IAB catheter 10.

[0040] FIGS. 5A-5C illustrate in detail alternate connections betweencatheter pressure sensor 22 and a distal end of pressure sensing line24. In FIG. 5A a distal end of pressure sensing line 24, extendingbeyond a distal end of either inner tube 58 (FIG. 3) or inner lumenextension tube 66 (FIG. 4), is stripped of insulation 72 exposing wires62. Catheter pressure sensor 22 comprises a transducer 74 connected to asupport 68. Exposed wires 62 are positioned over contacts 70 on support68 and may be soldered to support 68. Note that pressure sensing line 24is connected to inner tube 58 as shown in FIG. 3B, however, connectionsshown in FIGS. 3A and 3C may also be used.

[0041]FIG. 5B illustrates an alternate connection between the catheterpressure sensor 22 and the pressure sensing line 24 which is embedded ininner tube 58. This connection may be used when catheter pressure sensor22 is located in alternate location A (see FIGS. 3 and 4). Catheterpressure sensor 22 is identical to the embodiment in FIG. 5A exceptcontacts 70 are on the underside of the support 68. Wires 62 are exposedby peeling off insulation 72 and a portion of the inner tube 58 directlyabove pressure sensing line 24. Catheter pressure sensor 22 fitsdirectly on top of pressure sensing line 24 such that wires 62 fit overcontacts 70. Rather than stripping away an entire section of inner tube58, as in FIG. 5B, small holes 78 could be made over the ends of eachwire 62, as illustrated in FIG. 5C. Solder pads 76 project from an underside of catheter pressure sensor 22. Holes 78 can be alignedperpendicular to the longitudinal axis of the tube or if the wires arewound helically, see dotted lines in FIG. 5C, the holes can be alignedalong the longitudinal axis of the inner tube 58. Note that catheterpressure sensor 22 may shifted proximally such that it does not overhangthe distal end of inner tube 58. In such case, an additional holethrough inner tube 58 may be used to allow transducer 74, which isplaced over such hole, to communicate with inner lumen 60.

[0042] Alternatively, transducer 74 may face toward an outer surface ofcatheter tip 20 and sense pressure on the outside of tip 20. This can beaccomplished by using a thicker support 68 or by creating a pocket 90over transducer 74, as illustrated in FIG. 6. FIG. 6 is a longitudinalcross section of tip 20 and a distal end of inner tube 58 and balloonmembrane 30. Tip 20 has a pocket 90 directly over transducer 74. Pocket90 may contain a gel, fluid, gas, elastomer, or any other flexiblesubstance which both communicates pressure and protects transducer 74.Membrane 92 prevents leakage of gel or protective pocket 82. As analternative to the use of membrane 92, balloon membrane 30 can beextended to cover pocket 90. This catheter pressure sensor 22arrangement can be used for both the dual lumen (FIG. 3) and columencatheters (FIG. 4).

[0043] Note that for both the typical dual lumen and co-lumen catheterarrangements the portion of the inner tube 58 disposed within theballoon membrane 30 may be made from a different material from the restof the inner tube 58. This can be accomplished by connecting twoseparate pieces of tubing as disclosed in U.S. Pat. No. 6,024,693,assigned to Datascope Investment Corp., herein incorporated by referencein its entirety.

[0044] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A balloon catheter system comprising a ballooncatheter, a fluid-filled pressure measurement system, and a tip pressuresensor, said balloon catheter comprising a balloon membrane, a tip, aproximal fitting, an outer tube, and an inner tube disposed within anouter surface of said outer tube, said inner tube extending beyond adistal end of the outer tube, a distal end of the balloon membrane beingconnected to the tip and to a distal end of the inner tube, a proximalend of the inner tube and outer tube being connected to the proximalfitting, said tip pressure sensor connected to the tip, saidfluid-filled pressure measurement system comprising a fluid source,connected to the proximal fitting via a fluid source line, and apressure measurement means for measuring pressure in said fluid sourceline and in communicating inner tube.
 2. The balloon catheter system asclaimed in claim 1 wherein the pressure measurement means for measuringpressure in the fluid source line comprises a transducer.
 3. The ballooncatheter system as claimed in claim 1 further comprising a restrictionmeans between the fluid source and the fluid source line for controllingthe rate of drip of fluid from the fluid source into the fluid sourceline through the inner tube.
 4. The balloon catheter system as claimedin claim 3 wherein the fluid source comprises a bag of pressurizedsaline.
 5. The balloon catheter system as claimed in claim 1 wherein theinner tube and outer tube have a coaxial arrangement.
 6. The ballooncatheter system as claimed in claim 1 wherein the inner tube and outertube have a co-lumen arrangement.
 7. The balloon catheter system asclaimed in claim 1 wherein the inner tube is connected to the outertube.
 8. The balloon catheter system as claimed in claim 1 wherein thetip comprises a tip lumen communicating with said inner lumen, an outersurface, and a pocket in said outer surface, and wherein the tippressure sensor is embedded in the tip with at least one surface beingexposed in said pocket.
 9. The balloon catheter as claimed in claim 8wherein said pocket is filled with a protective material.
 10. Theballoon catheter as claimed in claim 9 wherein said protective materialis a gel.
 11. The balloon catheter as claimed in claim 8 wherein saidpocket is sealed by a membrane.
 12. The balloon catheter as claimed inclaim 8 wherein said pocket is sealed by a distal end of the balloonmembrane.
 13. A balloon catheter system comprising a balloon catheter, afluid-filled pressure measurement system, and a secondary catheter, saidballoon catheter comprising a balloon membrane, a tip, a proximalfitting, an outer tube, and an inner tube disposed within an outersurface of said outer tube, said inner tube extending beyond a distalend of the outer tube, a distal end of the balloon membrane beingconnected to the tip and to a distal end of the inner tube, a proximalend of the inner tube and outer tube being connected to the proximalfitting, said secondary catheter fitting within the inner tube andhaving a pressure sensor connected to a distal end, said fluid-filledpressure measurement system comprising a fluid source, connected to theproximal fitting via a fluid source line, and a pressure measurementmeans for measuring pressure in said fluid source line and incommunicating inner tube.
 14. A method for measuring pressure in abodily vessel comprising the steps of: a)inserting a balloon catheterinto said bodily vessel, said balloon catheter comprising a balloonmembrane, a tip, a tip pressure sensor connected to said tip, a proximalfitting, an outer tube, and an inner tube disposed within an outersurface of said outer tube, said inner tube extending beyond a distalend of the outer tube, a distal end of the balloon membrane beingconnected to the tip and to a distal end of the inner tube, a proximalend of the inner tube and outer tube being connected to the proximalfitting, said inner tube being connected to a fluid source line, saidfluid source line containing a fluid pressure sensor and being connectedto a fluid source, said fluid source delivering a slow drip of fluidthrough fluid source line and inner tube, said fluid pressure sensor andsaid tip pressure sensor communicating with a processor for computationof pressure based on signals generated by said tip pressure sensor andsaid fluid pressure sensor; b)measuring pressure over a period of timein the bodily vessel via the fluid pressure sensor; c)calculating a truemean pressure based on said fluid pressure sensor measurements;d)measuring pressure over the same period of time in the bodily vesselvia the tip pressure sensor; e)calculating an indicated mean pressurebased on said tip pressure sensor measurements; f)comparing the truemean pressure and the indicated mean pressure; g)outputting the tippressure sensor measurements adjusted by the difference between the twomean pressures if the true mean pressure is greater or less than theindicated mean pressure by a predetermined amount, otherwise outputtingthe tip pressure sensor measurements.
 15. A method for measuringpressure in a bodily vessel comprising the steps of: a)inserting aballoon catheter into said bodily vessel, said balloon cathetercomprising a balloon membrane, a tip, a tip pressure sensor connected tosaid tip, a proximal fitting, an outer tube, and an inner tube disposedwithin an outer surface of said outer tube, said inner tube extendingbeyond a distal end of the outer tube, a distal end of the balloonmembrane being connected to the tip and to a distal end of the innertube, a proximal end of the inner tube and outer tube being connected tothe proximal fitting, said inner tube being connected to a fluid sourceline, said fluid source line containing a fluid pressure sensor andbeing connected to a fluid source, said fluid source delivering a slowdrip of fluid through fluid source line and inner tube, said fluidpressure sensor and said tip pressure sensor communicating with aprocessor for computation of pressure based on signals generated by saidtip pressure sensor and said fluid pressure sensor; b)measuring pressureover a period of time in the bodily vessel via the fluid pressure sensorand the tip pressure sensor; c)outputting the tip pressure sensormeasurements; d)at a predetermined time interval comparing the tippressure sensor measurement to the fluid pressure sensor measurement, ifthe measurements are different by over a predetermined amount and if thefluid pressure measurements are within a predetermined range, thenoutputting the fluid pressure measurements; e)repeating steps (b) and(d) and outputting the fluid pressure measurements until the pressuremeasurements are within said predetermined amount, then outputting thetip pressure sensor measurements.
 16. A method for measuring pressure ina bodily vessel comprising the steps of: a)inserting a balloon catheterinto said bodily vessel, said balloon catheter comprising a balloonmembrane, a tip, a tip pressure sensor connected to said tip, a proximalfitting, an outer tube, and an inner tube disposed within an outersurface of said outer tube, said inner tube extending beyond a distalend of the outer tube, a distal end of the balloon membrane beingconnected to the tip and to a distal end of the inner tube, a proximalend of the inner tube and outer tube being connected to the proximalfitting, said inner tube being connected to a fluid source line, saidfluid source line containing a fluid pressure sensor and being connectedto a fluid source, said fluid source delivering a slow drip of fluidthrough fluid source line and inner tube, said fluid pressure sensor andsaid tip pressure sensor communicating with a processor for computationof pressure based on signals generated by said tip pressure sensor andsaid fluid pressure sensor; b)measuring pressure over a period of timein the bodily vessel via the tip pressure sensor; c)measuring thepressure in the bodily vessel at a predetermined time interval via thefluid pressure sensor; d)comparing the fluid pressure sensor measurementand the tip pressure sensor measurements; e)outputting the tip pressuresensor measurement adjusted by the difference between the twomeasurements if the fluid pressure sensor measurement is greater or lessthan the tip pressure sensor measurement by a predetermined amount,otherwise outputting the tip pressure sensor measurement.
 17. The methodas claimed in claims 13, 14, 15, or 16 wherein the bodily vesselcomprises a blood vessel and the pressure being measured being bloodpressure.e.
 18. The method as claimed in claims 13, 14, 15, or 16wherein the tip comprises a tip lumen communicating with said innerlumen, an outer surface, and a pocket in said outer surface, and whereinthe tip pressure sensor is embedded in the tip with at least one surfacebeing exposed in said pocket.
 19. An intra-aortic balloon pump systemcomprising an intra-aortic balloon pump, an intra-aortic ballooncatheter connected to said intra-aortic balloon pump, and an independentblood pressure measurement device connected to said intra-aortic balloonpump, said intra-aortic balloon catheter comprising an outer tube, aballoon membrane, and a tip, a proximal end of the balloon membranebeing connected to a distal end of the outer tube and a distal end ofthe balloon membrane being connected to the tip, said tip having a tippressure sensor connected to it and communicating with the intra-aorticballoon pump.
 20. The intra-aortic balloon pump system as claimed inclaim 19 wherein the independent blood pressure measurement devicecomprises a blood pressure cuff.
 21. A method for operating anintra-aortic balloon pump system comprising an intra-aortic balloon pumpand an intra-aortic balloon catheter, said intra-aortic balloon cathetercomprising a balloon membrane, a tip, a tip pressure sensor connected tosaid tip, a proximal fitting, an outer tube, and an inner tube disposedwithin an outer surface of said outer tube, said inner tube extendingbeyond a distal end of the outer tube, a distal end of the balloonmembrane being connected to the tip and to a distal end of the innertube, a proximal end of the inner tube and outer tube being connected tothe proximal fitting, said inner tube being connected to a fluid sourceline, said fluid source line containing a fluid pressure sensor andbeing connected to a fluid source, said fluid source delivering a slowdrip of fluid through fluid source line and inner tube, said fluidpressure sensor and said tip pressure sensor communicating with aprocessor communicating with the intra-aortic balloon pump forcomputation of pressure based on signals generated by said tip pressuresensor and said fluid pressure sensor, said method comprising the stepsof: a. Continuously measuring pressure via the tip pressure sensor; b.At predetermined time intervals adjusting pressure readings from the tippressure sensor based on readings from the fluid pressure sensor; c.Contracting the balloon membrane prior to cardiac ejection as determinedbased on the tip pressure sensor readings; d. Inflating the balloonmembrane coincident with closure of the aortic valve as indicated by thedicrotic notch of the tip pressure sensor readings; and e. Repeatingsteps a-d for the duration of therapy.
 22. A method for operating anintra-aortic balloon pump system comprising an intra-aortic balloon pumpand an intra-aortic balloon catheter, said intra-aortic balloon cathetercomprising a balloon membrane, a tip, a tip pressure sensor connected tosaid tip, a proximal fitting, an outer tube, and an inner tube disposedwithin an outer surface of said outer tube, said inner tube extendingbeyond a distal end of the outer tube, a distal end of the balloonmembrane being connected to the tip and to a distal end of the innertube, a proximal end of the inner tube and outer tube being connected tothe proximal fitting, said inner tube being connected to a fluid sourceline, said fluid source line containing a fluid pressure sensor andbeing connected to a fluid source, said fluid source delivering a slowdrip of fluid through fluid source line and inner tube, said fluidpressure sensor and said tip pressure sensor communicating with aprocessor communicating with the intra-aortic balloon pump forcomputation of pressure based on signals generated by said tip pressuresensor and said fluid pressure sensor, said method comprising the stepsof: a. Continuously measuring pressure via the tip pressure sensor; b.Continuously comparing each pressure reading from the tip pressuresensor with each pressure reading from the fluid pressure sensor andadjusting each tip pressure reading if a predetermined pressuredifferential exists between the tip pressure sensor reading and thefluid pressure sensor reading; c. Contracting the balloon membrane priorto cardiac ejection as determined based on the tip pressure sensorreadings; d. Inflating the balloon membrane coincident with closure ofthe aortic valve as indicated by the dicrotic notch of the tip pressuresensor readings; and e. Repeating steps a-d for the duration of therapy.23. A method for operating an intra-aortic balloon pump systemcomprising an intra-aortic balloon pump, an intra-aortic ballooncatheter connected to said intra-aortic balloon pump, and an independentblood pressure measurement device connected to said intra-aortic balloonpump, said intra-aortic balloon catheter comprising an outer tube, aballoon membrane, and a tip, a proximal end of the balloon membranebeing connected to a distal end of the outer tube and a distal end ofthe balloon membrane being connected to the tip, said tip having a tippressure sensor connected to it and communicating with the intra-aorticballoon pump. said method comprising the steps of: a. Continuouslymeasuring pressure via the tip pressure sensor; b. At predetermined timeintervals adjusting pressure readings from the tip pressure sensor basedon readings from the independent blood pressure measurement device; c.Contracting the balloon membrane prior to cardiac ejection as determinedbased on the tip pressure sensor readings; d. Inflating the balloonmembrane coincident with closure of the aortic valve as indicated by thedicrotic notch of the tip pressure sensor waveform; and e. Repeatingsteps a-d for the duration of therapy.
 24. The method as claimed inclaim 23 wherein the independent blood pressure measurement devicecomprises a blood pressure cuff.